(1) Field of the Invention
The present invention relates to a communication system enabling a communication device on one end and a communication device on the other end to communicate with each other via a relay device, and particularly to a communication system capable of notifying a communication device user of the fact that one of two or more radio channels is disconnected and restoring such disconnected radio channel in an optimal manner.
(2) Description of the Related Art
There is a conventional technology to automatically restore a communication line at the time of an abrupt disconnection of such communication line in a communication system in which communication devices connected via radio communicate with each other (See the Japanese Laid-Open Patent Application No. S61-21666).
The following explains such prior art with reference figures.
FIG. 1 is a block diagram showing a configuration of a conventional communication system. In FIG. 1, a communication system 90 is comprised of a communication device 91, a radio base station 14, a cellular network 13, an other communication device 15 and others.
The communication device 91 includes a displaying unit 191, an input unit 192, a central controlling unit 193, a network communicating unit 194, a number memory unit 195 and others, and a voice signal is inputted/outputted through a microphone 196 and a speaker 197. Furthermore, the communication device 91 is connected to the other communication device 15 via the radio base station 14 and the cellular network 13. Note that the internal configuration of the other communication device 15 is analogous to that of the communication device 91, and a voice signal is inputted/outputted through a microphone 151 and a speaker 152.
Next, an explanation is given for operations in the communication system 90 which is a conventional communication system with the above configuration.
FIG. 2 is a communication sequence diagram illustrating sequences in the communication system 90 shown in FIG. 1 from when a call starts to when a communication line is disconnected and restored.
First, an explanation is provided for an operation performed before a call starts between the communication device 91 and the other communication device 15. As shown in FIG. 2 a usual communication sequence before a call starts is that after a subscriber's number of the other communication device 15 is dialed by a user of the communication device 91 via the input unit 192 (See FIG. 1), an outgoing call request is transmitted to the radio base station 14, which is delivered to the other communication device 15 over the cellular network 13. When detecting a call from the communication device 91, the other communication device 15 outputs a call-accepted signal which is transmitted to the radio base station 14 over the cellular network 13, and the communication device 91 is notified of the completion of the connection. A call starts after the above-described sequence.
When there occurs a line failure in the middle of the call due to, for example, the communication device 91 moving out of the radio area covered by the radio base station 14, and it is detected that the line between the communication device 91 and the other communication device 15 is disconnected, the communication device 91 handles such disconnection by automatically re-calling the subscriber's number of other communication device 15 stored in the number memory unit 195. While the communication line is being restored, the displaying unit 191 of the communication device 91 shows the user that the line failure is being restored.
The communication system 90 explained hereinbefore is a conventional communication system intended only for a single radio channel. If such communication system is multi-connected via a relay device, that is to say, if a communication device on one end and a communication device on the other end are connected to each other via a plurality of radio channels, a line disconnection causes a problem described below.
Upon detection of the line disconnection, the user tries to perform an operation to restore a disconnected channel. However, since there exist two or more radio networks used for the communication, the user has trouble identifying which channel is disconnected and performs a wrong operation, trying to restore the channel as quickly as possible. In other words, such user, who hastily tires to perform a plurality of restoration operations which differ according to the type of a channel, conducts a wrong operation. This makes a problem especially in the case where a communication device used in such a situation is a hands-free device equipped in a car. In a radio hands-free system in which a communication device is a hands-free device and a relay device is a mobile phone, a call between such devices is conducted with the hands-free device and the mobile phone being connected to each other via such a local channel as Bluetooth, and with the mobile phone being connected to a radio base station via a cellular network. If there occurs an abrupt disconnection of one of the two channels, the user who is driving starts an operation to restore such disconnected channel. However, since it is difficult to identify which channel is disconnected, such user hastily tries to perform a plurality of restoration operations which differ depending on the type of a channel. As a result, the user's attention in driving is scattered, which affects his/her ability to drive safely.
In addition to the above, there is another technology which is as follows: in a communication system in which a plurality of subscribers' terminals are connected to a switchboard via an access device, if a breakdown occurs to the access device and such access device is initialized, causing all communication paths to be disconnected, the disconnected communication paths between the plurality of subscribers' terminals and the switchboard are restored to the state before the breakdown, on the basis of data stored in such switchboard (See the Japanese Laid-Open Patent Application No. H10-229420). This technology, however, is not intended for a disconnection of each channel in a plurality of multi-connected radio channels. Therefore, when one of such plurality of the channels is disconnected, it is difficult to identify the disconnected channel, which consequently results in an operating error of the user who is in haste to restore the channel as soon as possible, just like the above-mentioned case.